The Florida red tide, produced by the dinoflagellate Karen/a brevis, occurs almost annually and has adverse economic and health effects. Exposure of people to sea spray containing aerosolized K. brevis causes irritation of the eyes, nose, and throat, as well as bronchoconstriction in some individuals. In the first 5 years of the program project, we have developed methods to characterize red tide aerosol and to assess personal exposure. We have obtained information on the brevetoxin level produced by K. brevis on the beach and particle size distribution during exposure and non-exposure periods. We have developed dose estimates of the inhaled red tide aerosol and have showed an association of airborne brevetoxins to the observed respiratory effects. We also have shown that PbTx is a component of the marine aerosol generated from a wave-powered bubble mechanism. The concentration of PbTx aerosol during the red tide episodes is usually below 100 ng/m3, which is sufficient to increase respiratory symptoms in human subjects in an occupational exposure study and studies involving asthma patients as described in the the Project by Flaming. The measured red tide aerosol particle size is in the coarse particle mode (>1 mu m in diameter) with a mass median aerodynamic diameter between 6 to 9.6 (mu m. The dose estimate based on the measured particle size showed a total deposition fraction of 82 to 89% in the human respiratory tract. The majority of inhaled red tide aerosol deposited in the upper airway (nasal, oral, pharynx and larynx region) with small but not insignificant deposition (3 to 7%) in the lower airways. The inhaled red tide aerosol has high deposition efficiency in the respiratory tract and the pattern of deposition would help to explain the observed respiratory symptoms. Our dose estimate indicates that several ng of deposited PbTx in a certain region of the human respiratory tract could be associated with observed symptoms in upper airway and/or lower airway systems. Our dose estimate shows that exposure to air concentrations as low as 3 to 5 ng/m3 may be sufficient to relate to upper airway symptoms, and higher PbTx concentrations of 30-40 ng/m3 may be required to cause lower airway symptoms for asthmatics. It also shows that brevetoxin is one of the most potent substances associated with human respiratory effects. Our colleagues at the Toxin Probes and Assays continue to separate and identify compounds from K. brevis cultures with structures related to the brevetoxin. These include the new brevetoxins (PbTx-11,12), and brevenals (antagonists of respiratory effects). As these new compounds are identified, we also need to quantify them in red tide aerosol samples obtained in the field study. In addition, our results show temporal variation of the PbTx profile during the sampling period as environmental conditions change. Therefore, it will be useful to improve the assessment of personal exposure and local deposition pattern in the upper airway to relate the observed respiratory symptoms with individual exposure. Based on this new information, we propose to continue studies to further characterize red tide aerosol and to investigate the means to predict and minimize red tide aerosol exposure. The overall objectives of our proposed study are (1) to identify red tide aerosol components that may have implications for respiratory heath effects including PbTxs, antagonists, and congeners, (2) to improve assessment of personal exposure and biomarkers for exposure, (3) to improve the understanding of marine aerosol formation and transport processes, and (4) to develop a model of the red tide aerosol in the affected area. Information gained from these studies will aid in evaluation of human risk associated with inhalation of red tide aerosols, and provide a means to predict red tide aerosol events, which may help to minimize future exposures to red tide aerosol.